Real space transfer (RST) electronic devices are known to the art. See, for instance, "Heterojunction Band Discontinuities: Physics and Device Applications", F. Capasso et al., editors, Elsevier 1987, especially pages 513-537, incorporated herein by reference.
Known RST devices are a transistor, variously called charge-injection transistor (CHINT) or negative resistance field effect transistor (NERFET), and the hot-electron erasable programmable random access memory (HE.sup.2 PRAM). See, for instance, U.S. Pat. No. 4,903,092, also incorporated herein by reference.
Briefly, the CHINT is a three-terminal device based on real-space transfer of hot electrons from a first to a second conducting region. The two conducting regions are separated by a barrier region and are contacted independently, with the first conducting region having two surface contacts (frequently referred to as "source" and "drain"). Application of a source-to-drain bias V.sub.sd can lead to a heating of electrons in the first region and consequent charge injection into the second conducting region. The first region thus acts as a hot electron emitter and the second region as a collector. This terminology will generally be used herein.
A logic circuit that comprises prior art RST devices is known. For instance, on page 520 of the above referenced monograph is disclosed a logic circuit comprising two NERFETs.
Recently a novel RST logic element was disclosed. See U.S. patent application Ser. No. 07/514,078, filed Apr. 25, 1990 for S. Luryi et al., and incorporated herein by reference. The logic element has electrical inputs and an electrical output, and can, inter alia, make possible simplification of logic circuits. It can also make possible self-organizing logic, and can provide a logic function (XNOR) that previously could only be obtained by a combination of logic elements.
Semiconductor light emitting devices are well known. Among them are edge emitting lasers and surface emitting lasers (SELs). For a recent review of SELs, see, for instance, K. Iga et al., IEEE Journal of Quantum Electronics, Vol. QE-24, pp. 1845-1855 (1988), incorporated herein by reference. A particular and potentially advantageous type of SEL is known as "vertical cavity" SEL (VCSEL). In current pumped VCSELs the optical cavity is typically formed by two multilayer semiconductor "mirrors", with the injection current by necessity flowing through the mirrors. Typically the mirrors have relatively high electrical resistance, resulting inter alia in undesirable heat dissipation. Since SELs have the potential for significant use in, e.g., optical communications and optical computing, it would be desirable to have available a SEL that is not subject to this and other shortcomings of prior art SELs.
In many present and/or potential applications it is necessary to produce an optical output in response to an electrical input. Frequently the thus created optical signal will serve as an input for a logic element. It would clearly be of interest to have available a device whose optical output in response to electrical input signals can provide a non-trivial logic function (i.e., a logic function other than NOT), such that the light-emitting device is also a logic element. It would be of particular interest if the logic function provided by the element were a function that could previously not be realized with a single logic element.
Below will be disclosed a novel semiconductor light emitting device whose different embodiments can have these and other advantageous properties.